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The present invention relates to post-tensioning systems. More particularly, the present invention relates to post-tensioning systems having intermediate anchorages. Furthermore, the present invention relates to sealing devices for preventing liquid intrusion into the exposed sections of tendons in the post-tension system.
For many years, the design of concrete structures imitated the typical steel design of column, girder and beam. With technological advances in structural concrete, however, its own form began to evolve. Concrete has the advantages of lower cost than steel, of not requiring fireproofing, and of its plasticity, a quality that lends itself to free flowing or boldly massive architectural concepts. On the other hand, structural concrete, though quite capable of carrying almost any compressive load, is weak in carrying significant tensile loads. It becomes necessary, therefore, to add steel bars, called reinforcements, to concrete, thus allowing the concrete to carry the compressive forces and the steel to carry the tensile forces.
Structures of reinforced concrete may be constructed with load-bearing walls, but this method does not use the full potentialities of the concrete. The skeleton frame, in which the floors and roofs rest directly on exterior and interior reinforced-concrete columns, has proven to be most economic and popular. Reinforced-concrete framing is seemingly a quite simple form of construction. First, wood or steel forms are constructed in the sizes, positions, and shapes called for by engineering and design requirements. The steel reinforcing is then placed and held in position by wires at its intersections. Devices known as chairs and spacers are used to keep the reinforcing bars apart and raised off the form work. The size and number of the steel bars depends completely upon the imposed loads and the need to transfer these loads evenly throughout the building and down to the foundation. After the reinforcing is set in place, the concrete, a mixture of water, cement, sand, and stone or aggregate, of proportions calculated to produce the required strength, is placed, care being taken to prevent voids or honeycombs.
One of the simplest designs in concrete frames is the beam-and-slab. This system follows ordinary steel design that uses concrete beams that are cast integrally with the floor slabs. The beam-and-slab system is often used in apartment buildings and other structures where the beams are not visually objectionable and can be hidden. The reinforcement is simple and the forms for casting can be utilized over and over for the same shape. The system, therefore, produces an economically viable structure. With the development of flat-slab construction, exposed beams can be eliminated. In this system, reinforcing bars are projected at right angles and in two directions from every column supporting flat slabs spanning twelve or fifteen feet in both directions.
Reinforced concrete reaches its highest potentialities when it is used in pre-stressed or post-tensioned members. Spans as great as one hundred feet can be attained in members as deep as three feet for roof loads. The basic principle is simple. In pre-stressing, reinforcing rods of high tensile strength wires are stretched to a certain determined limit and then high-strength concrete is placed around them. When the concrete has set, it holds the steel in a tight grip, preventing slippage or sagging. Post-tensioning follows the same principle, but the reinforcing tendon, usually a steel cable, is held loosely in place while the concrete is placed around it. The reinforcing tendon is then stretched by hydraulic jacks and securely anchored into place. Pre-stressing is done with individual members in the shop and post-tensioning as part of the structure on the site.
In a typical tendon tensioning anchor assembly used in such post-tensioning operations, there are provided anchors for anchoring the ends of the cables suspended therebetween. In the course of tensioning the cable in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of each cable for applying a predetermined amount of tension to the tendon, which extends through the anchor. When the desired amount of tension is applied to the cable, wedges, threaded nuts, or the like, are used to capture the cable at the anchor plate and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition.
There are many post-tension systems employing intermediate anchorages where the length of the slab is too long to tension with a single anchor. In these systems, the intermediate anchor is interposed between a live end and a dead end anchor. In the construction of such intermediate anchorage systems, the tendon extends for a desired length to the intermediate anchor. A portion of the sheathing is removed in the vicinity of the intermediate anchor. The intermediate anchor is installed onto a form board in accordance with conventional practice. The unsheathed portion of the tendon is received by a tensioning apparatus such that the tendon is stressed in the area between the dead end anchor and the intermediate anchor. After stressing the tendon, concrete is poured over the exterior of the sheathed tendon and over the dead end anchor and intermediate anchor. The remaining portion of the tendon extends from the intermediate anchor to either another intermediate anchorage or to the live end anchor. Intermediate anchorage systems are employed whenever the slab is so long that a single live anchor extending to a single dead end anchor is inadequate. For example, two intermediate anchorages would be used for slabs having a length of approximately 300 feet.
A problem that affects many of the intermediate anchorage systems is the inability to effectively prevent liquid intrusion into the unsheathed portion of the tendon. Normally, the unsheathed portion will extend outwardly, for a distance, from the intermediate anchor in the direction toward the dead end anchor. Additionally, another unsheathed portion will extend outwardly at the intermediate anchor toward the live end anchor. In normal practice with a single live anchor and without intermediate anchors, a liquid-tight tubular member is placed onto an end of the anchor so as to cover the unsheathed portion of the tendon. This is relatively easy to accomplish since the length of the tendon is minimal at the live end. However, it is a considerable burden to attempt to slide such a tubular member along the entire length of the tendon so as to form the liquid-tight seal at the intermediate anchorage. In normal practice, tape, or other corrosion protection materials, are applied to the exposed portion of the tendon adjacent the intermediate anchorage. Extensive practice with this technique has shown that it is generally ineffective for preventing liquid intrusion into the interior of the tendon or into the interior of the intermediate anchorage. As such, a great need has developed in which to protect the exposed areas of the tendon adjacent the intermediate anchorage.
A problem inherent in such continuous tendon intermediate anchorage systems is the difficulty of installation. Conventionally, in order to install the great lengths of tendon associated with such an intermediate anchorage systems, it is necessary for the worker at the construction site to thread the anchor along the length of the tendon so as to place the anchor in a desired position. Often during this xe2x80x9cthreadingxe2x80x9d of the anchor onto the tendon, nicks and damage can occur to the sheathing on the tendon. Often, components of the intermediate anchorage system are omitted or the installation is carried out in an ineffective manner because of the large amount of manual manipulation that is required for the installation of the system. Inherently, each of the intermediate anchors will be located in a joint of the concrete structure. As such, each of the anchors will be exposed to the corroding elements in this location. The liquid resistance of the intermediate anchorage system must be particularly good so as to prevent any damage to the exposed portions of the tendon.
In one form of the installation of post-tension systems, a xe2x80x9csplice chuckxe2x80x9d is used so as to secure the end of one tendon to the end of a next in-line tendon. Conventionally, the splice chuck will be joined to the unsheathed portion of a first tendon and joined to the unsheathed portion of a second tendon. The use of wedges, springs and other components of the splice chuck will assure that one end of the first tendon is securely joined to the opposite end of the next in-line tendon. After the splice chuck is used to join the ends of the tendons in proper relationship, the concrete can be poured over the tendons and the splice chuck. Unfortunately, because of the use of springs, wedges and other components in the splice chuck, the splice chuck is particularly susceptible of corrosion and deterioration. The weakening of any component within the splice chuck, such as the spring, can cause the integrity of the splice chuck to become compromised and, possibly, release the end of one tendon from the end of an adjoining tendon. The exposure of the splice chuck to the corroding elements is particularly important since, as stated previously, the intermediate anchorage will inherently appear at a joint in the concrete structure.
The splice chuck can solve the problems associated with the extremely long strands or tendons throughout the concrete structure. In effect, shorter lengths of tendons can be installed and joined in secure end-to-end relationship by the use of a splice chuck. The anchors can be pre-installed onto the tendon prior to delivery to the construction site. The use of the splice chuck eliminates the need for workers to xe2x80x9cthreadxe2x80x9d the anchor, and the other components, along the extended lengths (up to five hundred feet) of the tendon. Unfortunately, the splice chucks have not been able to be used as part of an intermediate anchorage system in which encapsulated systems are required.
The present inventor is also the inventor of U.S. Pat. No. 6,151,850, issued on Nov. 28, 2000 and U.S. Pat. No. 6,176,051, issued on Jan. 23, 2001. Each of these patents describes intermediate anchorage systems utilizing splice chucks. U.S. Pat. No. 6,151,850 teaches a post-tension anchor system having a first tendon with a sheathed portion and an unsheathed portion, a second tendon having a sheathed portion and a unsheathed portion, an anchor receiving the first tendon therein so as to have unsheathed portion of the first tendon extending outwardly from one end of the anchor, and a splice chuck receiving the unsheathed portion of the first tendon at one end thereof and receiving the unsheathed portion of the second tendon at an opposite end thereof. The cover extends over the splice chuck so as to have one end extending in liquid-tight relationship with the sheathed portion of the second tendon. The cover also includes a cap member formed in an opposite end which is engaged within the cap-receiving section of the encapsulation of the anchor. The cover includes a polymeric section extending around a portion of the body of the splice chuck and the opposite end of the splice chuck, and an elastomeric portion extending around another portion of the body at the other end of the splice chuck. The elastomeric portion overlaps an end of the polymeric section in liquid-tight relationship therewith. U.S. Pat. No. 6,176,051 describes a similar type of configuration with the introduction of a cap member that includes a tubular section having an interior area and an annular section extending radially outwardly from an end of the tubular section. The annular surface contacts an end of the wedges associated with the tendon-receiving cavity.
Although these prior patent by the present inventor provide an excellent solution to the problems identified hereinbefore, there have been certain difficulties associated with the use of such splice chucks. Most importantly, it is difficult for inspectors to be absolutely assure that the tendons have been secured in their properly tensioned relationship within the splice chuck. Additionally, the arrangements of springs, cap members and other items sometimes presented a conceptually difficult arrangement for workers at the construction site to fully comprehend. Additionally, there are certain costs associated with the formation of such splice chucks which exceeded the desired costs associated with the components used for the formation of such intermediate connection.
It is an object of the present invention to provide a connector for an intermediate anchorage system which effectively prevents liquid intrusion into the post-tension anchorage system.
It is another object of the present invention to provide a connector assembly for an intermediate anchorage which is easy to install.
It is a further object of the present invention to provide a connector assembly which assures a proper seating of the ends of the post-tension tendons within the connector assembly.
It is still a further object of the present invention to provide a connector assembly which is easy to use, easy to manufacture and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is post-tension anchor comprising a first tendon having a sheathed portion and unsheathed portion, a second tendon having a sheathed portion and a unsheathed portion, a first anchor receiving the unsheathed portion of the first tendon therein, a second anchor receiving the unsheathed portion of the second tendon therein, a coupler extending over the first anchor and secured to the second anchor, and a cover extending over the exterior surface of the coupler. The unsheathed portion of the second tendon will extend outwardly beyond an end of the second anchor. The first tendon extends through a hole in the coupler. The cover is a polymeric encapsulation in liquid-tight relationship with the exterior surface of the coupler.
In particular, in the preferred embodiment of the present invention, the second anchor comprises a barrel anchor having a tendon-receiving cavity therein and encapsulation anchor positioned adjacent to the end of the barrel anchor. The unsheathed portion of the second tendon is secured within the tendon-receiving cavity of the barrel anchor. The encapsulation anchor has an interior passageway through which the second tendon extends. The cover is affixed in liquid-tight relationship to the encapsulation of the encapsulated anchor. The barrel anchor has threads formed on an exterior surface thereof. The coupler has threads formed on an interior surface thereof. The coupler is threadedly engaged with the barrel anchor.
In the present invention, the first anchor is also barrel anchor having a tendon-receiving cavity formed therein. The unsheathed portion of the first tendon is secured within the cavity of the barrel anchor. The tendon-receiving cavity of the first anchor is tapered so as to have a wide opening at one end thereof. The second anchor also has a tapered tendon-receiving cavity formed therein. The second tendon has an end of the unsheathed portion received within this cavity of the second anchor. The tapered tendon-receiving cavity of the second anchor has a wide opening at an end thereof adjacent the wide opening of the first anchor. The first tendon has a plurality of wedges interposed in interference-fit relationship between the unsheathed portion of the first tendon and a wall of the cavity of the first anchor. The second anchor has a plurality of wedges interposed in interference-fit relationship between the unsheathed portion of the second tendon and a wall of the cavity of the second anchor. A resilient member is interposed between the first anchor and the second anchor within the coupler so as to urge the first anchor toward an end of the coupler.
In the preferred embodiment of the present invention, the coupler is a tubular member having an open end and a closed end. The hole is formed in the closed end. The first anchor is positioned adjacent to the closed end. The second anchor has a portion extending outwardly of the open end. The cover is a polymeric encapsulation extending over the coupler. The cover has a portion extending beyond the open end of the coupler. This portion of the coupler is in liquid-tight sealing relationship with an exterior surface of the second anchor. Additionally, the cover has a tubular portion extending beyond the closed end of the coupler. This tubular portion is axially aligned with the hole at the closed end of the coupler.
In the present invention, a first sealing member is affixed to the cover and extends outwardly therefrom and around the first tendon. This first sealing member is in liquid-tight sealing relationship with the sheathed portion of the first tendon. A second sealing member is affixed to the second anchor and extends outwardly therefrom and around the second tendon. The second sealing member is in liquid-tight sealing relationship with the sheathed portion of the second tendon.
The present invention is also a method of forming an intermediate anchorage of a post-tension anchor system comprising the steps of: (1) encapsulating a coupler within a polymeric encapsulation extending in liquid-tight relationship thereover; (2) positioning a first anchor within the coupler such that the coupler has an open end and a closed end with a hole formed in the closed end; (3) forming a first anchor assembly having a first tendon affixed within the tendon-receiving cavity of the first anchor and such that the first tendon extends through the hole in the closed end of the coupler; (4) affixing a second tendon within the tendon-receiving cavity of the second anchor; and (5) securing the coupler to the second anchor such that the first and second tendons are axially aligned in end-to-end relationship. The polymeric encapsulation is in liquid-tight sealing relationship with the second anchor.
Also, in the method of the present invention, the step of affixing comprises affixing an end of the second tendon within a tendon-receiving cavity formed within the barrel anchor of the second anchor assembly. The step of securing comprises affixing a portion of the polymeric encapsulation to an exterior surface of the encapsulation of the encapsulated anchor. The step of securing further comprises threadedly securing the coupler to an exterior surface of the barrel anchor associated with the second anchor assembly. A resilient member is positioned between the first and second anchors within the couplers so as to resiliently urge the first anchor toward an end of the coupler.